How To Use UV Light To Increase THC?

Research shows a link between UV radiation and an increased THC content of marijuana. With this knowledge, we can increase our crop’s potency. Growers have realized an increase of up to 30% THC percentage by using supplemental UVB light but the actual mechanism was not well understood. Many growers have been aware of the benefits of UVB and have used supplemental lighting to boost potency. However, be aware, there is a threshold where the damage to yield caused by high level UVB will exceed any benefits in potency, so caution and careful design protocols MUST be used when attempting to supplement UVB. It is also VERY important to be EXTREMELY careful using off-the-shelf UVB lights that are not specifically designed for human exposure, because while sunlight has quite high levels of UVB, the intensity of the sun prevents people from staring straight at it. UVB is invisible, so your eyes can’t tell you if they are getting too much UVB from a UVB light source in your grow room, and your eyes and skin can be damaged if the levels are too high. So it’s worth repeating: Extreme caution must be observed when using secondary UVB supplementation.

LED Grow lights provide a special consideration when it comes to the effects of UVB on Cannabis THC levels. LEDs are extremely frequency specific, and a typical LED grow light with Blue, Red or even White LEDs will generate absolutely NO UVB radiation. While an absence of UVB does not appear to eliminate THC production, it is now proven that it will reduce the THC levels below those grown under sources with adequate UVB levels.

The exact purpose and role that cannabinoids such as THC and CBD have in cannabis plants is still not entirely understood. Research, however, suggests that cannabinoids are a type of natural defence mechanism. It is believed that cannabis plants produce cannabinoids to ward off and defend against pests, diseases, and ultraviolet radiation. As such, recent studies have theorised that increasing UV exposure could cause more cannabinoid production in cannabis as a defensive measure – increasing potency and resin production.

We know that the most potent weed that grows naturally can be found in elevated mountainous areas around the world. Worthy to mention here, would be the growing hashish production areas in the Rif Mountains of Morocco, the Beqaa Valley of Lebanon, and the Hindu Kush. These areas have several noteworthy things in common: they are all close to the 30 °N latitude on the globe, they have the perfect marijuana-growing climate, an abundance of sunshine, and most importantly, they are located at high altitude. This means that plants receive substantially higher amounts of UV radiation – the higher you go, the greater the exposure. UVB is a part of the sun’s natural light, so all outdoors plants get it to some degree.

Cannabis UV light

Knowing this, scientists have gone a step further. Researchers from Maryland did a comparison of cannabis plants grown with and without additional ultraviolet radiation exposure. It was found that certain cannabis strains that were already high in THC produced almost 28% more THC when exposed to UVB light. Oddly enough, the experiment did not lead to an increase of CBD in CBD-rich strains. These results strongly suggest a link between UVB radiation and THC, hinting at that increased THC production may play a role in protecting the plant from UV radiation.


Since we now know UVB radiation could greatly increase the potency of our crops, we can take advantage of this knowledge. With supplemental light bulbs that generate UVB radiation similar to natural UV light, we can supply greater amounts of UV light to our plants for increased potency.

Small and affordable UVB-emitting “reptile lights” can often be found in pet stores, as some reptiles need UV light. You can also do an internet search for those types of supplemental UV lamps. Some newer grow lights may even come with an integrated UV light. For the average micro or mini grow-op, those supplemental UV lights don’t have to be large. A single reptile light (or “desert light” as they are sometimes called) can be sufficient if you want to supplement some UV light to boost your crops’ THC content. Outdoors, there is little you can do to boost UV, other than grow up a mountain! Either way, the fact that UV could play an important role is an interesting discovery, showing just how much we still have to learn about this wondrous plant!

  • Are you searching for cannabis seeds? Check out our seed store – well worth checking out!

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